Opiates and opioid peptides modify immune function. Thus, exposure to opiates may be a cofactor determining susceptibility to HIV infection. This application focuses on cellular and molecular studies designed to elucidate basic mechanisms underlying the influence of opioid peptides on immune function. Two elements of the mechanism under investigation are: (1) the physicochemical and functional characterization of naloxone-resistant binding sites on normal immune cells which may mediate many of the effects of B-endorphin; (2) induction within normal immune cells of mRNAs coding for prepro-enkephalin-A and proopiomelanocortin, precursors to the enkephalins and B-endorphin. Characterization of naloxone-resistant B-endorphin binding sites will involve radioligand binding studies to determine the Kd, Bmax, competition characteristics, conditions of induction and cell subpopulations expressing the binding site from normal splenocyte and thymocyte preparations. Physicochemical characterization will involve covalent crosslinking of [125 I]-B-endorphin to the binding site followed by analysis on SDS-PAGE. Sucrose density gradient analysis without crosslinking will also be performed. To establish the functional significance of this binding site, a concanavalin-A dependent thymocyte proliferation assay and thymocyte helper cell assay will be used to characterize: (1) induction of the binding site; (2) dose-dependence of binding site activation; (3) selective activation of the binding site by fragments of B-endorphin and other opioids; and (4) cell subpopulations which are proximate targets of binding site activation. Studies of opioid peptide mRNA expression in thymocytes and splenocytes will focus on the inductive effects of infection with murine hepatitis virus (MHV) A59, a natural murine pathogen. The dose-response, kinetic relations, cell subpopulations affected, and requirement for live versus killed MHV will be determined in vivo. In vitro experiments will evaluate whether interleukin-lB mediates the effect of MHV on mRNA expression. Finally, immunohistochemical studies will assess whether opioid translation products are present in immune cells after MHV infection. These studies of the naloxone-resistant receptor and the expression of mRNAs coding for opioid peptides will help define a paracrine system whereby immune cells produce and respond to opioid peptides.